1. Field of the Invention
The present invention relates to a method for manufacturing a dispersion of a quinoline derivative that is suitable for a variety of functional substance materials.
2. Description of the Related Art
Agricultural chemicals, such as herbicides and insecticides, drugs, such as anticancer drugs, antiallergic drugs, and antiinflammation agents, and colorants, such as inks and toners containing coloration agents, are well known examples of dispersion materials containing functional substances. Among these materials, quinoline compounds are known as intermediates for agricultural chemicals and drugs and also as organic electroluminescent (EL) materials. They have also found a wide application as colorants, and some of them are known to be used as pigments. A remarkable progress has been achieved in recent years in the field of digital printing technology. Electrophotography and ink jet technology are typical representative of digital printing technology, and the presence thereof as imaging technology in offices and homes has recently become more and more noticeable.
A direct recording method, as one of the ink jet methods, can be implemented with compact equipment and features low power consumption.
Further, miniaturization of nozzles has rapidly advanced the quality of images. In one of the methods representing ink jet technology, ink supplied from an ink tank is evaporated and bubbled by heating with a heater located in a nozzle and the ink is ejected to form an image on a recording medium. In another example, ink is ejected from a nozzle by inducing oscillations with a piezo element.
The ink used in these methods is typically in the form of an aqueous dye solution. As a result, bleeding can occur in the zones where colors overlap, or a phenomenon called feathering sometimes occurs in the paper fiber direction in the recording locations on the recording medium. U.S. Pat. No. 5,085,698 discloses using a pigment dispersion ink to overcome these drawbacks.
However, in most cases, the pigment dispersion inks are inferior to dye inks in terms of coloration ability. Thus, because pigment particles cause color scattering and color reflection, the coloration ability of images formed by pigment inks is generally inferior to that of the images obtained with dye inks. Further, coarse pigment particles cause nozzle clogging in the ink jet head.
Decreasing the size of the pigment particles has been attempted as a method for overcoming the above-described drawbacks of pigment inks. Pigments reduced in size to 100 nm or less demonstrate a low level of light scattering and have a larger surface area. This should result in an improvement in coloration ability. However, conventional methods have been unable to solve the problems associated with this approach.
Pigment dispersion ink is typically obtained by dispersing a usual water-insoluble organic pigment in an aqueous medium. This process includes a step of adding the pigment to an aqueous medium containing a dispersant and then finely grinding in a dispersion apparatus, such as a sand mill or a ball mill, using hard beads. A substantial problem associated with such process is how to obtain a fine and stable pigment dispersion.
Japanese Patent Laid-open No. 9-176543 discloses a method for obtaining an organic pigment particle dispersion with a particle size equal to or less than 100 nm via a high-speed mill dispersion using beads. While a fine dispersion can be reliably obtained using this method, a large amount of energy is required for the dispersion process. Also, a complex process is necessary to separate the obtained dispersion liquid from the beads.
On the other hand, a method for obtaining fine particles of a pigment by dissolving the pigment and then precipitating it again has been suggested.
Japanese Patent Laid-Open No. 9-221616 suggests producing fine particles by an acid pasting method in which an organic pigment is dissolved using sulfuric acid. However, this method fails to produce pigments with a particle size of 100 nm or less.
Japanese Patent Publication Nos. 5-27664 and 6-96679 and Japanese Patent Laid-Open No. 11-130974 describe methods for obtaining fine pigment particles by dissolving an organic pigment together with a dispersant in an aprotic polar solvent in the presence of an alkali and then neutralizing with an acid and precipitating the pigment.
In these methods, poorly soluble pigments are dissolved. Therefore, the amount of the solvent necessary for dissolving the pigment is large, which makes a high-concentration dispersion difficult to produce.
In the first embodiment of Japanese Patent Publication No. 6-96679, 300 parts of dimethylsulfoxide is used per 30 parts of a pigment. Using a large amount of organic solvent increases not only the cost of production, but can also increase the cost of the wastewater treatment. Furthermore, although the dispersion obtained can be concentrated by distilling the solvent off under reduced pressure or by ultrafiltration, a significant amount of effort and time are still required for obtaining a high-concentration dispersion.
In sum, in the manufacture of pigment dispersions using the above-described conventional re-precipitation method, more specifically, a method in which a pigment solution is mixed with a liquid that decreases the solubility of the pigment and pigment particles are precipitated, a large amount of solvent is required because of poor solubility of the pigment and a high-concentration dispersion is difficult to manufacture.
Japanese Patent Laid-Open No. 2005-307154 discloses a method for producing 2,9-dimethylquinacridone by a synthesis using a capillary as a reactor.
In this synthesis reaction, a starting material is mixed with p-toluenesulfonic acid, dimethylformamide and ethylene glycol, the mixed solution is passed through a capillary heated in an oil bath, and 2,9-dimethylquinacridone is synthesized.
However, since p-toluenesulfonic acid is solid at normal temperature, it is difficult to pass it through a capillary. Also, because a solvent is used, it is typically difficult to obtain 2,9-dimethylquinacridone at a high concentration. Furthermore, in order to obtain 2,9-dimethylquinacridone using water as a dispersion medium, a phase transition to water is necessary, and there is a risk of causing an additional decrease in concentration.
Moreover, when the synthesis is performed in the presence of a dispersant, there is also a risk that the dispersant will dissolve at a high temperature under acidic conditions, thereby limiting a number of suitable dispersants.